A compressor includes one or more rotating discs (rotor or wheel), bladed or not, and one or more wheels with fixed vanes (straightener stages).
A radial (or centrifugal) compressor has at least one radial compressor stage, that is capable of achieving a flow of gas perpendicular to the central axis of the compressor. It includes at least one wheel with radial blades which aspirate the air axially which, under the influence of the radial force, is accelerated, compressed and driven out radially. This air is then straightened in a diffuser (fixed vanes) which transforms part of its speed into static pressure by slowing the gases leaving the wheel. The operation must take place with a minimum of total pressure loss while still maintaining a satisfactory level of stability of the compressor so as to maintain an acceptable surge margin for operation of the turbomachine.
The gases are then guided toward the combustion chamber.
A mixed-flow (or axial-radial) compressor has at least one compression stage diagonal with respect to said central axis, so that the fluid leaves the wheel of the compressor forming a nonzero angle with the radial direction.
A diffuser of a radial compressor consists of a wheel made up of two flanges between which the gases flow radially or diagonally from the center toward the periphery. Vanes are distributed between the flanges along the entire wheel. These vanes form a flow cascade between the leading edges of these vanes and the trailing edges.
However, deflection of the air flow leaving the wheel by the vanes of the diffuser can cause separation of the fluid on the intrados or the extrados of the vanes, which separation, if it is considerable, can lead to stalling of the fluid and, as a result, of pumping. It is known that this pumping phenomenon is harmful to the elements constituting the compressor, so that one seeks to avoid it to the extent possible.
Usually, the vanes of the diffuser consist of an intrados wall and an extrados wall with a circular arc shape, and include a quasi-linear right angle. An example of such a vane is illustrated in FIG. 1. However, these vanes have a limitation in terms of diffusing capacity. Indeed, an increase in diffusion by these vanes causes a drop in isotropic efficiency and an increase in the instability of the compressor.
A diffuser for a radial compressor including vanes conforming to the preamble of claim 1 was proposed in document WO 2012/019650. In particular, this document describes vanes the profile whereof has a camber line defined by a function having an inflection point. For this reason, the camber line has an “S” shape and makes it possible to distribute loads along the profile of the vane, with a low loading in the area of the leading edge, which increases progressively up to the inflection point of the vane, where it is a maximum. However, the use of such a vane showing such an “S” profile requires limiting the cross-section at the diffuser throat (that is at the fluid entry cross-section). This has the effect of shifting the Flow rate/Rate characteristic toward lower flow rates, and reduces the aerodynamic choking flow of the diffuser.
Vanes with a profile curve similar in shape to an “S” have also been described in document JP 2011-252424. In particular, the vanes of this document are configured so that an angle formed between the line of curvature and the circumferential profile curve rises, then drops, then rises again between the leading edge and the trailing edge of the vane. Here too, the cross-section at the diffuser's throat must therefore be limited, which has the effect of reducing the stability of the diffuser.